1. Field of the Invention
The present invention relates to fibre channel systems, and more particularly to configuring fibre channel ports.
2. Background of the Invention
Fibre channel is a set of American National Standard Institute (ANSI) standards, which provide a serial transmission protocol for storage and network protocols such as HIPPI, SCSI, IP, ATM and others. Fibre channel provides an input/output interface to meet the requirements of both channel and network users.
Fibre channel supports three different topologies: point-to-point, arbitrated loop and fibre channel fabric. The point-to-point topology attaches two devices directly. The arbitrated loop topology attaches devices in a loop. The fibre channel fabric topology attaches host systems directly to a fabric, which are then connected to multiple devices. The fibre channel fabric topology allows several media types to be interconnected.
Fibre channel is a closed system that relies on multiple ports to exchange information on attributes and characteristics to determine if the ports can operate together. If the ports can work together, they define the criteria under which they communicate.
In fibre channel, a path is established between two nodes where the path's primary task is to transport data from one point to another at high speed with low latency, performing only simple error detection in hardware.
Fibre channel fabric devices include a node port or “N_Port” that manages fabric connections. The N_port establishes a connection to a fabric element (e.g., a switch) having a fabric port or F_port. Fabric elements include the intelligence to handle routing, error detection, recovery, and similar management functions.
A fibre channel switch is a multi-port device where each port manages a simple point-to-point connection between itself and its attached system. Each port can be attached to a server, peripheral, I/O subsystem, bridge, hub, router, or even another switch. A switch receives messages from one port and automatically routes it to another port. Multiple calls or data transfers happen concurrently through the multi-port fibre channel switch.
Fibre channel switches use memory buffers to hold frames received and sent across a network. Associated with these buffers are credits, which are the number of frames that a buffer can hold per fabric port.
Fibre channel links/ports can operate (i.e. receive and/or transmit data) in different speeds, for example, 1 gigabit per second (“G”), 2 G, 4 G, 8 G and now 10 G. 10 G ports can be implemented using a single link supporting a serial stream of 10.5 G serial data stream or by four physical lanes of 3.1875 G serial data stream where each lane carries 1 byte of a 4-byte transmitted word.
The base clock rate for 10 G ports is not an even multiple of 1 G/2 G/4 G/8 G rate, which means that conventional 100 ports cannot easily be scaled down to operate at 1 G/2 G/4 G/8 G. Although 10 G as a standard is gaining popularity, there are many legacy devices that still operate and will continue to operate at lower data rates (1 G/2 G/4 G/8 G).
Typically, 1 G/2 G/4 G ports use a standard fibre Channel negotiation procedure to support a particular speed, allowing for example, a 4 G port to negotiate with a 1 G or 2 G port. However, this negotiation procedure is not available for a 10 G port per the current fibre channel standards, which will allow a 10 G port to operate at a lower rate.
Therefore, it is desirable to have a single fibre channel switch element on a single chip that can handle high 10 G throughput and be configured to operate at lower rates, for example, 1 G/2 G/4 G/8 G.